Catheter apparatus and methodology for generating a fistula on-demand between closely associated blood vessels at a prechosen anatomic site in-vivo

ABSTRACT

The present invention provides catheter apparatus and catheterization methodology for generating an arteriovenous fistula or a veno-venous fistula on-demand between closely associated blood vessels and at a chosen anatomic site in-vivo. The catheter apparatus is preferably employed in pairs, each catheter of the pair being suitable for percutaneous introduction into and extension through a blood vessel. The catheterization methodology employs the catheter apparatus preferably in conjunction with conventional radiological techniques in order to place, verify, and confirm a proper alignment, orientation, and positioning for the catheters in-vivo prior to activating the perforation means for generating a fistula. The invention permits the generation of arteriovenous fistulae and veno-venous fistulae anatomically anywhere in the vascular system of a patient; nevertheless, the invention is most desirably employed in the peripheral vascular system as exists in the extremities of the body to aid in the treatment of the patient under a variety of different medical ailments and pathologies.

This is a Divisional of application Ser. No. 08/616,588, filed on Mar.15, 1996 now U.S. Pat. No. 5,830,224.

FIELD OF THE INVENTION

The present invention is concerned with improvements in catheter designand usage in-vivo; and is particularly directed to catheterizationapparatus and methods for creating an arteriovenous fistula or aveno-venous fistula between adjacently positioned blood vessels.

BACKGROUND OF THE INVENTION

A catheter is a long flexible tube introduced into a blood vessel or ahollow organ for the purpose of introducing or removing fluids;implanting medical devices; or for performing diagnostic tests ortherapeutic interventions. Catheters are conventionally known andfrequently used; and a wide range and variety of catheters are availablewhich are extremely diverse in shape, design and specific features.

Typically a catheter is a long thin tube of fixed axial length, with twodiscrete, unique ends. One end is designed and engineered to be insertedin the body; the other end generally remains outside the body, and is sodesigned. Most catheters have at least one internal lumen of a volumesufficient to allow for on-demand passage of a diverse range of wires,rods, liquids, gases, transmitting energy, fiber optics, andspecifically designed medical instruments.

The fundamental principles and requirements for constructing a guidingflexible catheter exist as conventional knowledge in the relevanttechnical field; and all of the essential information is publicly known,widely disseminated, and published in a variety of authoritative texts.The medical and technical literature thus provides an in-depth knowledgeand understanding of the diagnostic and therapeutic uses of conventionalcatheters and commonly used catheterization techniques. Merelyrepresentative of the diversity of publications now publicly availableare the following, each of which is expressly incorporated by referencehere: Diagnostic And Therapeutic Cardiac Catheterization, second edition(Pepine, Hill, and Lambert, editors), Williams & Wilkins, 1994 and thereferences cited therein; A Practical Guide To Cardiac Pacing, fourthedition (Moses et. al., editors), Little, Brown, and Company, 1995 andthe references cited therein; Abrams Angiography, third edition (H. L.Abrams, editor), Little, Brown & Co., 1983; Dialysis Therapy, secondedition (Nissenson & Fine, editors), Hanley & Belfus Inc., 1992; andHandbook of Dialysis, second edition (Daugirdas & Ing, editors), Little,Brown and Co., 1994.

Thus, in accordance with established principles of conventional catheterconstruction, the axial length of the catheter may be composed of onesingle layer or of several layers in combination. In most multilayeredconstructions, one hollow tube is stretched over another tube to form abond; and the components of the individual layers determine the overallcharacteristics for the catheter as a unitary construction. Manymultilayered catheters comprise an inner tube of Teflon, over which isanother layer of nylon, woven Dacron, or stainless steel braiding. Atube of polyethylene or polyurethane typically is then heated andextruded over the two inner layers to form a firm bond as the thirdexternal layer. Other catheter constructions may consist of apolyurethane inner core, covered by a layer of stainless steel braiding,and a third external jacket layer formed of polyurethane.

In addition, a number of dual-lumen catheters are known today whichdiffer primarily in the size and spatial relationship between theirindividual lumens. Typically, a dual-lumen catheter can take manydifferent forms such as: two co-axially positioned lumens where onesmall diameter tube extends axially through the internal volume of alarger diameter tube; or the catheter is a single large diameter tubeand has a centrally disposed inner septum which divides the interiorvolume into two equal or unequal internal lumens; or where the materialsubstance of the catheter tube contains two discrete bore holes ofdiffering diameters which serve as two internal lumens of unequal volumelying in parallel over the axial length of the catheter. All of thesevariations present different dual-lumen constructions for cathetershaving a similar or identical overall diameter size.

Catheters are generally sized by external and internal diameter andlength. The internal diameter is specified either by actual diameter (inthousandths of an inch or millimeters or French size). Many newerthin-walled catheter designs provide a much larger internal lumen volumeto external diameter ratio than has been previously achieved; this hasresulted in catheters which can accommodate much more volume and allowthe passage of much larger sized articles through the internal lumen.External diameter is typically expressed in French sizes which areobtained by multiplying the actual diameter of the catheter inmillimeters by a factor of 3.1415 (π). Conversely, by traditional habit,the actual size of any catheter in millimeters may be calculated bydividing its French size by a factor of π. As an illustration of sizeusage. French sizes from 4-8 are currently used for diagnosticangiography. In addition, because of the variation between standard,thin-walled, and super high-flow catheter construction designs, a widevariety of external and internal lumen diameter sizes exist today.

In order to perform effectively in specialized medical procedures and inparticular anatomical areas, specific categories or classes of cathetershave been developed. Among the presently known specific types ofcatheters are: peritoneal catheters employed for peritoneal dialysis andwhich provide dialysate inflow and outflow for the removal of theby-products of metabolism from the blood; acute and chronic urinarycatheters introduced into the bladder, the urethra, or directly into therenal pelvis for the removal of urine; central venous catheters aredesigned for insertion into the internal jugular or subclavian vein;right heart catheters such as the Cournand and Swans-Ganz cathetersdesigned specifically for right heart catheterization; transeptalcatheters developed specifically for crossing from right to left atriumthrough the interatrial septum at the fossa ovalis; angiographiccatheters which are used for right or left ventriculography andangiography in any of the major vessels; coronary angiographic catheterswhich include the different series of grouping including Sones, Judkins,Amplatz, multipurpose, and bypass graft catheters; as well as manyothers developed for specific purposes and medical conditions.

An illustrative and representative example of traditional catheter usageis provided by the medical specialty of hemodialysis--the process bywhich extra water and toxic metabolites are removed from the blood by adialysis machine when the kidneys are impaired by illness or injury. Asummary review therefore of renal insufficiency or failure, thetechnique of hemodialysis, and the role of specialized catheters inmachine dialysis will demonstrate and evidence conventional limitations.

A wide variety of pathological processes can affect the kidneys. Someresult in rapid but transient cessation of renal function. In patientsso affected, temporary artificial filtration of the blood is sometimesnecessary. With time, renal function gradually improves and may approachnormal; and dialysis is therefore usually required only for a shortduration. The time required for the kidneys to recover will depend onthe nature and severity of the injury which typically varies from a fewdays to several months Thus, if the acute condition lasts for more thanthree or four days, the patient will probably require hemodialysis atleast once while awaiting return of renal function.

Other pathological conditions result in a gradual deterioration of renalfunction over months or years. These patients can go for quite some timebefore toxic concentrations of metabolites accumulate. Once they reachthe stage where dialysis is necessary, however, it is usually requiredfor the rest of their lives. Some of these patients retain low levels ofrenal filtration and can therefore be dialyzed as infrequently as once aweek. Many progress to total renal failure and require hemodialysis twoor three times each week. Still other types of renal injury result inrapid onset of permanent renal failure necessitating life long dialysis.

The dialysis machine serves as an artificial kidney to reduce harmfulconcentrations of the by-products of metabolism and to remove excesswater from the blood. The machine is essentially a special filter inseries with a blood pump. The filter is connected to the patient via twoblood lines. Blood drains from the patient to the dialysis machinethrough the afferent line; and a volume displacement pump providessuction to assist drainage. The same pump pressurizes the blood toovercome the resistance imposed by the filter. The filter makes use of asemipermeable membrane which separates the blood path from that ofdialysate, a special buffered solution used to clear filteredsubstances. Unwanted molecules diffuse through the semipermiablemembrane into the rapidly flowing dialysate and are carried out of thefilter in a manner analogous to that of urine flowing through a renaltubule. The membrane is incorporated as multiple pleated sheets or smallcaliber tubes to increase the surface area across which diffusion maytake place. Blood leaving the filter returns to the patient through thesecond, or efferent, blood line.

The ability to perform dialysis effectively is dependent on high flow ofblood through the filter. Furthermore, blood must be returned to thepatient as rapidly as it is withdrawn to prevent the hemodynamicconsequences of large fluctuations in intravascular volume. It istherefore necessary that both afferent and efferent blood conduits beconnected to the patient by way of transcutaneous catheters insertedinto large bore, high flow blood vessels.

For patients in whom renal recovery is anticipated, percutaneousintravenous access is used frequently. This technique makes use of alarge bore flexible two-lumen catheter. This catheter, measuring 10French, (roughly 3 mm in diameter) is introduced into the central venouscirculation via the subclavian or internal jugular vein. Placement oftranscutaneous venipuncture in conjunction with the Seldinger techniqueand serial dilation is used; and the tip of the catheter is positionedat the junction of the superior vena cava and the right atrium.Alternatively, the catheter is placed percutaneously in the femoralvein. Blood is withdrawn from one lumen and returned through the other.The afferent lumen ends 2 or 3 centimeters from the catheter tip whichinhibits recirculation of efferent blood. The large size and high bloodflow of the superior vena cava permits very effective dialysis with thistechnique.

Unfortunately, however, this method of percutaneous intravenous accessis not well suited for patients who will require long term or permanentdialysis. The presence of a foreign body (the access catheter) breachingthe skin is associated with a high risk of infection. This riskincreases with time, and in long term applications, is prohibitive.Because the foreign body is in an intravascular location, the infectionis usually associated with sepsis, or infection of the blood stream,which can be lethal. Special catheters are designed to be implanted or"tunneled" subcutaneously for several centimeters to decrease theincidence of sepsis; and if absolutely sterile technique is used whenmanipulating the catheter (and the skin exit site is meticulouslycleaned and dressed), these tunneled catheters can be used for severalmonths without incident. Despite pristine care, however, infection isinevitable with extended use; and all such catheters eventually must beremoved. Aside from sepsis, long term central venous access is alsoassociated with a time related increase in the risk of endocarditis,cardiac perforation from catheter tip erosion, and superior vena cavathrombosis. Patients who require permanent or lifetime hemodialysistherefore must be attached to the dialysis machine in a different way.

Two methods have evolved to provide long term vascular access inpatients on permanent dialysis. The first method involves surgicallyimplanting a 6 or 8 mm dacron or gortex tube graft subcutaneously in theupper extremity. A small transverse incision is made in the proximalforearm, just below the crease. One end of the tube graft is anastomosedto the side of the brachial artery and the other, to the side of a largeantecubital vein. The body of the graft between the two anastomoses istunneled just below the skin in a horseshoe configuration, with the bendat the mid forearm. Blood flowing through the tube bypasses thecapillary bed, and as such, represents a very low resistance pathway.This surgically created "short circuit" in the circulatory system isreferred to as a shunt. The low resistance in the shunt results in ahigh blood flow. To perform hemodialysis, two large bore needles aresterilely introduced into the graft lumen through the intact skin. Thiscan be readily accomplished as the graft, in its subcutaneous location,is easily palpated. The large lumen and high blood flow provideexcellent drainage for dialysis. After hemodialysis is completed, theneedles are removed, so no permanent breech in the skin exists. Eachtime the patient is dialyzed, needles are reintroduced.

The second method involves the creation of a direct arteriovenousfistula between the radial artery and an adjacent vein without the useof a prosthetic graft material. Once again, the capillary network isbypassed, and a low resistance "short circuit" in the circulatory systemresults. The direct and increased volume of blood flow through thefistula leads to massive venous dilation. Dialysis catheters are thenintroduced into the dilated veins.

To create an arteriovenous fistula for permanent hemodialysis, anincision is made at the wrist and the radial artery identified andmobilized. An adjacent vein is mobilized as well. After obtainingvascular isolation with vessel loops or soft clamps, the artery and veinare opened longitudinally for a distance of 5 to 8 mm. Using finemonofilament suture and magnified visualization, the arteriotomy andvenotomy are sewn together, creating a side-to-side anastomosis (or,alternatively, the end of the vein is sewn to the side of the artery).This surgically created connection allows blood to bypass the capillarybed, and results in dramatically increased flow through the forearmveins. In contrast to the shunt technique of the first method, there isno easily palpable prosthetic graft just beneath the skin that can beentered transcutaneously. However, because the arteriovenous fistula isperformed at the wrist, the thin-walled forearm veins are subjected tohigh blood flow; and, over a short period of time, dilate to 2-3 timestheir initial size. The massively dilated veins are easily identifiedand can be accessed by two large bore needles as described above for theshunt.

Each of the two surgical techniques has relative advantages anddisadvantages. The shunt, although simple to construct, involvesimplantation of a foreign body. Each time a needle is introducedpercutaneously, there is risk of infection of the graft with skinorganisms. The risk of infection is not as great as was described forthe indwelling intravenous dialysis catheters, but is still present.With meticulous attention to sterile technique, shunts of this type canbe maintained for years. Hemodialysis patients often have impairedimmune systems, however, and infection requiring shunt removal is notuncommon. A second problem seen with prosthetic shunts is that ofthrombosis necessitating thrombectomy or revision. Reactions take placebetween the prosthetic material and the platelets in the blood thatresult in liberation of clotting factors. These factors stimulateabnormal growth of the intima, or lining of the vein, at the venousanastomosis. This abnormal growth narrows the anastomosis resulting indecreased flow through the graft and thrombosis. Hemodialysis patientsoften require multiple operations for thrombectomy and shunt revisionthroughout their lives to maintain vascular access.

The direct arteriovenous fistula method is highly desirable andadvantageous in that no prosthetic material is implanted; and the riskof infection is therefore dramatically reduced. In addition, all bloodcarrying surface are lined with living intima, and intimal proliferationis very uncommon. Moreover, the vein, being composed of living tissue,has the ability to mend itself and is less likely to formpseudoaneurysms as is occasionally seen with prosthetic shunts afterextended use. For these reasons, most surgeons prefer to perform thisprocedure when it is technically feasible.

Unfortunately, in many patients, use of an arteriovenous fistula istechnically not possible by conventional means. As described above, theradial artery is dissected out at the wrist; and a distal dissectionzone is preferred in that more veins will be subjected to increased flowand dilation, resulting in more potential sites for hemodialysis needleinsertion. However, the radial artery is somewhat small at this distallocation which makes anastomosis technically more demanding, especiallyin smaller patients. Furthermore, because a direct anastomosis must beconstructed, a relatively large vein is needed in the immediate vicinityof the radial artery, and this is not always present. In thealternative, if a vein more than a centimeter away is mobilized andbrought over to the artery, venous kinking can occur which results indecreased flow and early thrombosis. In addition, mobilization of thevein disrupts the tenuous vasovasorum, the miniscule arteries thatprovide blood supply to the vein wal itself, which can result infibrosis of the vein wall and constriction of the vein lumen. This setsthe conditions for early fistula failure.

Note also that each of the procedures described above must be done inthe operating room. Most of the patients thus receive intravenoussedation and must be monitored postoperatively in a recovery roomenvironment. Some remain hospitalized for a day or more as per thesurgeon's preference. It is well known that individuals with renalfailure exhibit impaired wound healing and a compromised immunefunction. These patients are therefore at increased risk for developingpostoperative wound complications.

The conventional and limited usage of specialized catheters asexemplified by the medical practice of hemodialysis is thus welldemonstrated and revealed. Clearly, despite the recognized desirabilityand advantage of creating an arteriovenous fistula for long-term orlife-use patients needing dialysis, the use of catheters has remainedlimited and used primarily for the introduction and removal of fluidswhile the creation of arteriovenous fistulae remains the result ofskilled surgical effort alone. Thus, although there is a long standingand well recognized need for an improved procedure and/or vehicle forgenerating arteriovenous fistulae, no meaningful alternative has beendeveloped to date; and no catheter-based methodology or protocol hasever been envisioned as suitable for on-demand generation of anarteriovenous fistula in-vivo.

SUMMARY OF THE INVENTION

The present invention has multiple aspects and formats. One aspect ofthe invention provides a catheter for generating an arteriovenousfistula or a veno-venous fistula on-demand between closely associatedblood vessels at a chosen anatomic site in-vivo, said catheter beingsuitable for percutaneous introduction into and extension through ablood vessel and comprising:

(a) a tube having a fixed axial length, a discrete proximal end, adiscrete distal end, and at least one internal lumen of predeterminedvolume;

(b) a distal end tip adapted for intravascular guidance of said tubethrough a blood vessel in-vivo to a chosen anatomic site;

(c) magnet means positioned at said discrete distal end and set in axialalignment with said distal end tip of said tube, said magnet meanshaving sufficient magnetic force to cause an adjustment in position forsaid tube when in proximity with a source of magnetic attractiondisposed within a closely associated blood vessel;

(d) vascular wall perforation means positioned at said discrete distalend adjacent to said magnet means and set in axial alignment with saiddistal end of said catheter, said magnet means having sufficientmagnetic strength to cause an adjustment in position for said catheterwhen in proximity with an alternative source of magnetic attractiondisposed within a closely associated blood vessel;

(d) vascular wall perforation means positioned at said discrete distalend adjacent to said magnet means and set in axial alignment with saiddistal end tip of said tube, said vascular wall perforation meansbecoming intravascularly adjusted in position via the magnetic force ofsaid magnet means when in proximity with a source of magnetic attractiondisposed within a closely associated blood vessel in-vivo; and

(e) means for activating said vascular wall perforation means of saidtube on-demand wherein said vascular wall perforation means perforatesthe chosen anatomic site to generate a fistula in-vivo between theclosely associated blood vessels.

A second aspect of the present invention provides a catheterizationmethod for generating an arteriovenous fistula or a veno-venous fistulaon-demand between closely associated blood vessels at a chosen anatomicsite in-vivo, said catheterization method comprising the steps of:

procuring at least one catheter suitable for percutaneous introductioninto and extension through a blood vessel in-vivo to a chosen anatomicsite, said catheter being comprised of

(a) a tube having a fixed axial length, a discrete proximal end, adiscrete distal end, and at least one internal lumen of predeterminedvolume,

(b) a distal end tip adapted for intravascular guidance of said tubethrough a blood vessel in-vivo to a chosen anatomic site,

(c) magnet means positioned at said discrete distal end and set in axialalignment with said distal end tip of said tube, said magnet meanshaving sufficient magnetic force to cause an intravascular adjustment inposition for said catheter when in proximity with a source of magneticattraction disposed within a closely associated blood vessel in-vivo.

(d) vascular wall perforation means positioned at said discrete distalend adjacent to said magnet means and set in axial alignment with saiddistal end tip of said tube, said vascular wall perforation meansbecoming intravascularly adjusted in position via the magnetic force ofsaid magnet means when in proximity with a source of magnetic attractiondisposed within a closely associated blood vessel in-vivo,

(e) means for activating said vascular wall perforation means of saidcatheter on-demand wherein said vascular wall perforation meansperforates a chosen anatomic site in-vivo between closely associatedblood vessels;

percutaneously introducing said catheter into a first blood vessel andextending said catheter intravascularly to a chosen anatomic siteadjacent to a closely associated blood vessel;

percutaneously introducing a source of magnetic attraction into aclosely associated second blood vessel and extending said source ofmagnetic attraction intravascularly to the chosen anatomic site to be intransvascular proximity to said extended catheter;

permitting a transvascular magnetic attraction to occur between saidmagnetic means of said extended catheter in the first blood vessel andsaid source of magnetic attraction in the closely associated secondblood vessel whereby said vascular wall perforation means of saidcatheter comes into transvascular alignment with the closely associatedsecond blood vessel; and then

activating said vascular wall perforation means of said catheteron-demand wherein said vascular wall perforation means perforate thevascular walls of said closely associated blood vessels concurrently atthe chosen anatomic site to generate a fistula in-vivo.

BRIEF DESCRIPTION OF THE FIGURES

The present invention may be more completely and easily understood whentaken in conjunction with the accompanying drawing, in which:

FIGS. 1A-1E illustrate of the modified Seldinger technique as a seriesof manipulative steps;

FIG. 2 is an overhead view showing a preferred embodiment of a venouscatheter used to generate an arteriovenous fistula;

FIG. 3 is an overhead view showing a preferred embodiment of an arterialcatheter used to generate an arteriovenous fistula;

FIG. 4 is an overhead view of the venous introducer cylinder forming acomponent part of the preferred venous catheter of FIG. 2;

FIG. 5 is an overhead view of the venous obturator fitting into theintroducer cylinder of FIG. 4 and forming a component part of thepreferred venous catheter of FIG. 2;

FIG. 6 is an overhead view of the venous introducer cylinder of FIG. 4and the venous obturator of FIG. 5 in combination;

FIG. 7 is an overhead view of the tubular cutting tool forming acomponent part of the preferred venous catheter of FIG. 2;

FIG. 8 is a partial sectional view of the distal end of the tubularcutting tool of FIG. 7;

FIGS. 9A-9D are sequential sectional views demonstrating the consequenceof activating the vascular well perforation means in the tubular cuttingtool of FIG. 7;

FIG. 10 is an overhead view showing the venous introducer cylinder ofFIG. 4 and the tubular cutting tool of FIG. 7 in combination;

FIG. 11 is a side view of the distal end of the arterial catheter ofFIG. 3;

FIG. 12 is a partial sectional view of the preferred venous catheter ofFIG. 2 and the preferred arterial catheter of FIG. 3 in proper parallelalignment as a consequence of magnetic attraction and interaction;

FIG. 13 is a side view of the distal end of a second alternativeembodiment of a catheter suitable for generating an arteriovenousfistula in-vivo;

FIG. 14 is an axial-section view of the alternative catheter embodimentof FIG. 13;

FIG. 15 is a cross-section view of the second alternative catheterembodiment of FIG. 13 along the axis YY';

FIG. 16 is an axial-section view of a pair of alternative embodimentcatheters in proper parallel alignment for generating an arteriovenousfistula;

FIG. 17 is an illustration of the vascular system in the human forearmin which an intravascular ultrasound probe has been extended into theradial artery;

FIG. 18 is an illustration of an intravascular ultrasound-created imageshowing the radial artery wall and the adjacently positioned veins usingthe probe of FIG. 17;

FIG. 19 is an illustration of an extended intravascular ultrasound probewithin the radial artery at a site of arterial-venous proximity;

FIG. 20 is an illustration of an ultrasound-created image showing theradial artery wall and immediately adjacent veins using the probe ofFIG. 19;

FIG. 21 is an illustration showing the percutaneous introduction of avenous cylinder-obturator complex and its placement near the ultrasoundprobe in the radial artery;

FIG. 22 is an illustration of an ultrasound-created image showing theexistence of the venous cylinder-obturator complexed in the selectedvein at the site of arterial-venous proximity;

FIG. 23 is an illustration showing the venous catheter and the arterialcatheter in the adjacent blood vessels under simulated in-vivoconditions;

FIG. 24 is an illustration of a fluoroscopic-created image showing thealignment between the venous catheter and the arterial catheter of FIG.23;

FIG. 25 is a sectional view of the alignment overlap between the distalend of the venous catheter and the distal end of the arterial catheterunder simulated in-vivo conditions; and

FIG. 26 is a cross-section illustration of the aligned venous catheterand arterial catheter showing the act of perforating vascular walls togenerate an arteriovenous fistula.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

The present invention is a percutaneous arteriovenous fistula catheter(hereinafter "PAVFC") apparatus and methodology which will generate afistula between an adjacently located artery and vein or an adjacentlylocated pair of veins in the peripheral vascular system. Thearteriovenous (hereinafter "AV") fistula or veno-venous fistula(hereinafter "VV") is created in a controlled manner between closelyassociated blood vessels, ideally in the distal extremities (arms orlegs) of the patient. However, usage at any anatomic site is possible;and the AV (or VV) fistula can be generated on-demand at a prechosenvascular site under carefully monitored clinical conditions. As such,the present invention provides multiple advantages and unique benefitsto both the physician and the patient, some of which include thefollowing.

1. The present invention is not a surgical procedure as such. To thecontrary, the PAVFC apparatus and methodology is a radiologicaltechnique which avoids the use of surgical incisions and procedures andeliminates the need for surgically created AV (and VV) fistulas. It iswell recognized that chronically ill patients such as renal failurepatients have an impaired wound healing capacity; are subject to anincreased incidence of infection after surgery; and are subject to ahigh risk of hemorrhage as a consequence of surgical procedures. Thepresent invention permits the generation of AV (or VV) fistulas withoutnecessitating surgery or surgical incision, thereby reducing the risk tothe chronically ill patient. In addition, by the avoidance of surgicalprocedures as such, the need for an operating room, an anesthesiologist,and surgical nursing staff is obviated.

2. The present invention allows for AV or VV fistula formation inanatomical areas where surgical procedures would be difficult, if notimpossible, to perform. For example, in hemodialysis, surgical accessfor the creation of an AV fistula is often limited to the distal radialartery. However, often there is not an adjacently positioned or closelyassociated distal vein of sufficient size in the same anatomical areawhich is surgically accessible. In comparison, the PAVFC techniquecomprising the present invention generates fistula in the peripheralvascular system between closely associated arteries and veins wheretraditional surgical exposure would be impossible in most instances.Accordingly, the present invention allows for and has the potential toutilize many more vascular sites in the peripheral circulation aslocations for the generation of an AV fistula on-demand.

3. The present invention allows for the identification and evaluation ofjuxtapositioned blood vessels in the entire extremity (preferably by useof intravascular ultrasound to identify the most favorable anatomicalsite) in order to provide an accurate assessment of venous diameter at aspecific vascular site prior to performing the technique to generate anAV or VV fistula. Peripheral veins of small diameter or having thinwalls which are typically unsuitable for surgical anastomosis are easilylocated and now become available for use; and the determination ofwhether or not a portion of the venous vascular wall is closelyassociated with and lies adjacent to an artery (or vein) can beroutinely made.

4. The present apparatus and methodology allows the radiologist todetermine with substantial certainty whether or not a suitable veinexists in the vicinity of a closely associated peripheral artery (orvein) prior to beginning the requisite sequence of steps necessary togenerate a fistula. Not only is the juxtapositional determination made,but also the specific site is chosen in advance which provides the bestcombination of anatomical circumstances (including anatomic location,arterial venous proximity, arterial diameter, and venous diameter). Inthis manner, the radiologist may thoroughly consider a given vascularsite for generating the fistula; determine whether or not to seek a morefavorable location in the same closely associated vein and artery or inanother artery and vein in the same extremity; or whether to redirectthe catheter apparatus into another extremity in order to find a morefavorable anatomical site.

5. The apparatus and method of the present invention also provide a mostimportant benefit in that the blood vessels are not dissected out ormanipulated as a prerequisite of AV fistula formation. The tenuous vasovasorum therefore remains preserved in the naturally occurring state, acircumstance which improves vascular patency. This benefit stands incontrast to the loss of the vaso vasorum and other undesirableconsequences of vascular manipulation necessitated by conventionalsurgical AV or VV fistula creation which cause injury to the delicatevein wall and result in contraction of the vein--a condition whichlimits the vein's ability to dilate and may contribute to early fistulafailure. Moreover, although introducing the catheter of the presentinvention into a vein may be traumatic to the venous endothelium at thesite of entry, the injured segment of the vein will be distal to the AVfistula, and patency of this injured segment is not necessary for properfistula function. In addition, as the procedure for fistula formation isperformed at sites of close arterial venous approximation, no venousdistortion or kinking occurs or is necessary in the creation of thefistula.

6. The present invention provides far less risk to the critically orchronically ill patient in comparison to conventional surgicalprocedures for creation of AV (or VV) fistulae. The PAVFC techniqueoffers fewer potential problems than routinely occur with conventionalsurgical procedures; and these relatively few potential problems relateprimarily to the risk of hemorrhage. However, even this potential riskof hemorrhage is deemed to be small; is clinically obvious if and whenit occurs; and is readily controlled with direct pressure using aconventional blood pressure cuff or manual compression.

7. The present invention is intended to be employed in multiple usecircumstances and medical applications. An envisioned and particularlydesirable circumstance of usage is to provide long term vascular accessfor hemodialysis for those patients requiring permanent or long termdialysis. Additionally, the PAVFC technique can be used to create AVfistulae for the administration of caustic chemotherapeutic agents. Ineach of these instances, the PAVFC technique will not only identify oneor more favorable vascular sites in the radial and ulnar arteries alongtheir peripheral length, but also will identify other adjacentlypositioned veins and the most desirable anatomical sites within theclosely associated vein, particularly when lying within the distalportion of the forearm. In addition to these particular usages, thepresent invention allows for the generation of an AV or VV fistula forany other medical purpose, condition, or circumstance. Thus, the PAVFCtechnique can also be desirably used for creation of additional vascularinterconnections in the peripheral blood circulation between arteriesand veins; to generate a greatly enlarged blood vessel segment in theperipheral vascular system which then would be surgically excised andemployed as a vascular bypass graft or harvested on a pedicle in anotheranatomical area; and to generate on-demand alternative blood circulationpathways between arteries and veins in the peripheral vascular systemwhen blockages and other vascular obstructions exist.

In order to facilitate ease of understanding and to provide a completeand comprehensive description of the present invention in all itsaspects, a detailed disclosure of the catheter apparatus and methodologywill be presented in separate sections seriatim. The presentation willbe made in the following sequence: A description of the theoreticalsupport for the technique; a summary of conventional procedures forsurgically introducing and routing a catheter into the body of a livinghuman; a description of the preferred and several alternative catheterembodiments comprising the present invention; an illustrative exampleshowing the intended usage of the catheter apparatus in-vivo; and arepresentative description of some intended applications and usecircumstances for the present invention. Taken cumulatively andcollectively, the entirety of the disclosure not only describesembodiments of the preferred and alternative catheter apparatus but alsoenables the reader to make and use the present invention productivelywithout major difficulty or doubt.

I. Theoretical Support for the Invention

The present invention intends and expects the radiologist or attendingphysician to create a fistula in-vivo between an adjacently positionedand closely associated vein and artery (or between two closelyassociated veins) in the peripheral vascular system of a chronic orcritically ill patient. In effect and result, therefore, the presentinvention generates a direct flow connection between a functioningartery and vein (or between two functioning veins) without the existenceor usage of intervening capillaries.

To generate the AV fistula, the present invention perforates theimmediately adjacent vascular walls of both the vein and the arteryconcurrently, directly, and in tandem. Moreover, unlike conventionalsurgical procedures to create fistulas and shunts, there are no suturesused to join the vascular walls at the point of perforation; and nosynthetic or artificially introduced means for joining or attaching theperforated vein to the perforated artery are employed in order to obtainhemostasis at the point of anastomosis. It may therefore seemcounterintuitive to the reader that an AV fistula can be generated asdescribed without exsanguination into the arm or leg of the patient andwithout risk of blood loss or even death as a consequence of performingthe methodology.

The principle that enables an arteriovenous fistula to be created inthis way, however, is clearly demonstrated clinically and is encounteredfrequently. Unintended acquired arteriovenous fistulas are encounteredoccasionally in evaluation of patients with penetrating trauma such asknife stabbings, gun-shot holes, and other perforations of the bodycaused by violent acts. Physical exam of the wound in these individualsdemonstrates venous engorgement of the involved extremity in conjunctionwith an audible bruit or even a palpable venous thrill. Subsequentarteriogram of the wound area demonstrates an arteriovenous fistula inthe vicinity of the knife or missile tract. Other patients also withvascular injury after penetrating trauma, however, do not developarteriovenous fistulae. Most of these patients are found instead to havea pulsatile mass without pronounced venous engorgement; and anarteriogram of these patients demonstrates a pseudoaneurysm or containedrupture of the injured vessel. Note that these two types of injuries arealmost never seen in tandem. It is extremely unusual for a patient withan arteriovenous connection to have a pseudoaneurysm, and vice-versa.Similarly, some patients develop an arteriovenous connection between thecommon femoral artery and the femoral or saphenous vein as acomplication of percutaneous arterial access, whereas others developpseudoaneurysms; but the two clinical findings are almost never seentogether in one patient. Yet all of these patients are similar in thatthey have sustained substantial injury to a sizable artery. Thedifference in clinical findings thus lies in the spatial relationshipexisting between the injured blood vessels in-vivo.

In each example cited above, the patient has sustained an arterialvascular injury, either by knife, bullet, or angiographic needle. Thetissues surrounding the peripheral artery are adherent to the adventia(or outer layer of the artery wall), but can be dissected off by anexpanding hematoma. The blood extravasating through the arterial injurydoes so at arterial pressure which provides the force necessary for thecontinued expansion. The hematoma (or clotted blood collection) lyseswithin a day or two, leaving a juxta-arterial cavity that communicateswith the vessel lumen. The resulting clinical finding is that ofpseudoaneurysm. In some patients, however, there is also a closelyassociated venous injury concurrent with the arterial damage. If thevenous injury is of sufficient size and appropriate orientation, anarteriovenous fistula results. Blood leaves the artery through thearterial injury; flows along the knife or missile tract; and enters intothe vein through the venous injury. Moreover, because the venous systemhas such low resistance, the hydrodynamic pressure generated in thevicinity of the injury is not sufficient to cause a dissecting hematoma.The high flow velocity between the artery and vein maintains the patencyof the fistula thereafter.

It can be properly believed that every penetrating injury to anextremity is associated with multiple arterial and venous injuries ofvarious sizes. The likelihood of developing an arteriovenous fistulaafter penetrating injury is thus related to the caliber of the bloodvessels injured and the vascular geometry of the injury. If clean,linear perforations are made in immediately adjacent walls of 34 mmblood vessels, a fistula would almost certainly develop; andextravasation and pseudoaneurysm formation would be most improbable andhighly unlikely.

The present invention thus relies on this clinical basis for support;provides a catheter apparatus and a methodology by which to accessadjacently located arteries and veins in the extremities; and presentsthe means by which to generate a perforation on-demand at a chosenanatomic site in the peripheral vascular system between a closelyassociated artery and vein such that an aperture or hole is bored orotherwise created concurrently through both the adjacent arterial andvenous walls. A direct blood flow connection is thus generated by whicharterial blood passes through the perforation in the arterial wall andinto the vein lumen, through the aligned perforation in the immediatelyadjacent, low resistance vein. The underlying principle and basis isclinically established and documented; and there is no meaningful doubtor uncertainty that an AV fistula can be created on demand and in-vivowithin the extremities of the patient in a safe and reliable mannerusing the apparatus of the present invention, standard catheterizationtechniques, and conventionally known radiological procedures.

II. Surgical Introduction and Routing of a Catheter Into the Body of theLiving Human

Catheterization involves a great deal of technical skill, complexinstrumentation and mature judgment in order to choose among theappropriate procedures and the various techniques which are nowconventionally known and commonly available. Clearly, because thepresent PAVFC technique utilizes catheter intervention in critically orchronically ill patients, the physician must be very familiar with theavailable anatomical alternatives for accessing the peripheral vascularsystem in order to select the best site for introducing the catheter,the best route to the desired area of the body, and the optimal timingand other operative conditions in order to achieve the best results.

Catheterization as a general technique can be performed using any duct,tube, channel, or passageway occurring naturally or surgically createdfor the specific purpose. Thus, among the naturally occurringpassageways are the anus; the alimentary canal; the mouth, ear, nose, orthroat; a bronchus; the urethra; the vaginal canal and/or cervix; andany blood vessel. However, clearly the most common used and criticalroute of access for the present invention is the introduction ofcatheters into the vascular system. For this reason, it is useful todescribe conventional guiding catheters, and to briefly summarize thetechnique currently in use for introduction of catheters into thevascular system as an illustrative example of general catheterizationtechniques.

Catheter introduction techniques

There are two general methods currently in use for catheterization.These are: (a) percutaneous introduction using needles and guidewires;and (b) direct introduction after surgical isolation of the blood vesselof choice. While either general method may be utilized at any site ofthe vascular system, practical and anatomical considerations willgenerally dictate which approach is most appropriate under theindividual circumstances. Most often, however, the modified Seldingertechnique is favored for use.

The percutaneous introduction of a catheter is best illustrated by themodified Seldinger technique which is conventionally known and shown byFIGS. 1A-1F. FIG. 1A shows a blood vessel being punctured with a smallgauge needle. Once vigorous blood return occurs, a flexible guidewire isplaced into the blood vessel via the needle as shown by FIG. 1B. Theneedle is then removed from the blood vessel, the guidewire is left inplace, and the hole in the skin around the guidewire is enlarged with ascalpel as shown by FIG. 1C. Subsequently, a sheath and a dilator isplaced over the guidewire as shown by FIG. 1D. Thereafter, the sheathand dilator is advanced over the guidewire directly into the bloodvessel as shown by FIG. 1E. Finally, the dilator and guidewire isremoved while the sheath remains in the blood vessel as illustrated byFIG. 1F. The catheter is then inserted through the sheath and fedthrough the blood vessel to reach the desired location.

The other general method for the introduction of catheters into theblood circulation is direct surgical cutdown. The surgical cutdownapproach is generally used for the brachial approach or the femoralapproach. Cutdown procedure is often a complex surgical procedure and isused only when percutaneous arterial puncture (as described above) hasbeen unsuccessfully attempted. A far more complex and fully descriptivereview of both these general catheterization techniques is provided bythe texts of: Diagnostic And Therapeutic Cardiac Catheterization, secondedition, 1994, Chapter eight, pages 90-110 and the references citedtherein.

Accordingly, for purposes of practicing the present methodology, any andall generally known catheterization procedures, apparatus, andtechniques which are conventionally employed and are in accordance withgood medical practice are explicitly intended to be utilized asnecessary in their original format or in a modified form. All of thesegeneral catheterization routing and use techniques are thus envisionedand are deemed to be within the scope of the present invention.

General rules for choosing an appropriate site of body entry:

An axiomatic or general set of rules by which a physician can choose aproper or appropriate site of entry for introducing a guiding catheterinto the vascular system of a patient for purposes of performingdiagnostic tests or therapeutic interventions in-vivo is as follows: (a)always pick the shortest and straightest pathway possible or available;(b) identify the patency of an existing and accessible artery or vein,the larger the diameter of the blood vessel the better; and (c) avoidarteries with obvious calcification or atheromatous involvement.

A favored approach to introducing the catheter into the body:

(1) The intended site for entry is prepared and draped in a sterilefashion.

(2) The skin over the large bore artery or vein is infiltrated with 1%lidocaine for local anesthesia.

(3) A small skin nick is made over the anesthetized area.

(4) Via the skin nick, the large bore artery or vein is punctured usinga single wall puncture needle.

(5) The amount and nature of blood returning through the needle isevaluated for proper needle position.

(6) A 0.035 inch or 0.038 inch guide wire is passed via the needle intothe blood vessel.

(7) A 4-9 French dilator is passed coaxially over the wire and then isremoved.

(8) A hemostatic 4-9 French introducer sheath and obturator are passedcoaxially over the wire; and the obturator and wire are then removed.

(9) Via the hemostatic introducer sheath, the guiding catheter is passedthrough the blood vessel and located at the intended use site.

The description provided herein is merely a summary review of the meansand manner by which a catheter is properly introduced into the body of aliving human patient. The physician is presumed to be well acquaintedand sufficiently experienced in all these general catheterizationtechniques; and the choices of which manner or mode or usage ispreferable to another must be left to the medical discretion andjudgment of the physician given the specific problems and ailments ofhis patient.

III. The Unique Catheter Apparatus

The catheter apparatus comprising the present invention can take manydifferent and alternative forms and be constructed in a diverse range ofwidely different embodiments. As a favored approach, it is generallydesirable that the catheter apparatus comprise two discrete cathetersintroduced into the body independently but employed in tandem in orderto generate an AV fistula in-vivo. Nevertheless, in certain limitedmedical instances and under demanding medical circumstances, it is bothenvisioned and acceptable to employ a single catheter alone forpercutaneous introduction and extension through a vein or artery inorder to generate an AV fistula on-demand. Thus, although the use of asingle catheter independently is the least desirable format and mode ofusage of the present invention, the single catheter construction andusage nevertheless will serve and provide the means for generating an AVfistula between an adjacently positioned artery and vein at a chosenanatomic site in-vivo. However, if the physician has a choice given theparticular circumstances and ailments of his patient, it is far moredesirable that a pair of catheters be employed concurrently and intandem in order to achieve a far greater degree of certainty andreliability in the outcome.

A. A Preferred First Embodiment

A highly preferred embodiment of the catheter apparatus able to generatean AV fistula on-demand between a closely associated artery and vein ata chosen anatomic site in-vivo employs a pair of uniquely constructedcatheters concurrently and in-tandem. The first catheter of the pair issuitable for percutaneous introduction and extension through a veinin-vivo to a chosen intravenous location and is illustrated by FIG. 2.As exemplified by FIG. 2, a venous catheter 10 is seen having a hollowtubular wall 12 of fixed axial length; an interlocking proximal end 14for the catheter 10; a discrete distal end 16 and a co-axial internallumen 18 which extends from the interlocking proximal end 14 to thedistal end 16. Other features of the venous catheter are describedhereinafter.

The second of the pair in this preferred embodiment of the catheterapparatus is exemplified by FIG. 3 which illustrates a second cathetersuitable for percutaneous introduction into and extension through anartery in-vivo to a chosen intraarterial site. As exemplified by FIG. 3,an arterial catheter 200 is seen having a hollow tubular wall 202 offixed axial length; two proximal portals 204, 206 which together form adiscrete proximal end 208 for entry into the internal volume of thecatheter 200; a single discrete distal portal 210 for passage of aguidewire; and a discrete distal end 212; and an internal lumen 214.Additional details for the arterial catheter are described hereinafter.

In this preferred embodiment, the construction, some specific features,and the designated purpose for each catheter in the pair are markedlydifferent. While each catheter in the pair share common features forpurposes of location finding and placement intravascularly, thispreferred embodiment of the apparatus employs the venous catheter as theactive source and physical means by which the vascular walls areperforated in order to generate an AV fistula. In contrast, the intendedarterial catheter serves as a passive source of reinforcement, ofalignment, and of abutment intravascularly. Due to these differentfunctions and construction features, the details of each catheter in thepair will be described in detail independent from the other.

The construction and organization of the venous catheter

The essential component parts and their interrelationship is illustratedby FIGS. 4-8 respectively. As seen therein, FIG. 4 shows a hollowintroducer cylinder 20 which is a thin wall tube having a large diameterinternal lumen 22. The proximal end 24 is configured as a lockingarrangement 26 comprising two anti-rotation support bars 28, 30, aninterlocking notch 32, and a flat interlocking surface 34. The internallumen 22 extends through the entirety of the locking arrangement 26. Incomparison, the distal end 36 terminates as a planar surface 38 andcontains a cutout slot 40 in the tubular wall of the introducer cylinder20. The internal lumen 22 extends through the planar surface 38 at thedistal end 36; and the cutout slot 40 exposes a portion of the internallumen volume to the ambient environment.

A component part of the venous catheter is the internal obturator shownby FIG. 5. An obturator, by definition, is a structure which closes orstops up an opening such as a foramen or internal lumen. As illustratedwithin FIG. 5, the obturator 50 is an extended rod-like hollow shaft offixed axial length but having an external shaft diameter which isslightly smaller in size than the internal lumen 22 of the introducercylinder 20 of FIG. 4. The obturator 50 has a small diameter internallumen 52 which continues axially from the proximal end 54 to the distalend 56. The proximal end 54 is purposely configured as a semi-circulardisc 58 having a extended finger portion 60. The small diameter internallumen 52 of the obturator 50 extends through the semicircular discportion 58 as shown. In comparison, the distal end 56 terminates as atapered end tip 62 and contains a portal 64 of sufficient size for aconventional guidewire to pass there through into the lumen 52.

It is intended and expected that the obturator 50 of FIG. 5 will befitted into the proximal end 24 of the introducer cylinder 20(illustrated by FIG. 4) and be extended through the large diameterinternal lumen 22 along the entire axial length to form acylinder-obturator composite as shown by FIG. 6. As seen therein, thelocking arrangement 26 at the proximal end of the introducer cylinder 20interlocks with the extended finger 60 and semi-circular disc 58 of theobturator 50 to form a composite proximal end 70. Similarly, the distaltapered end tip 62 of the obturator 50 passes through the distal end 38of the cylinder 20 to form a composite distal end 72. Note that in thiscomposite orientation illustrated by FIG. 6, the small diameter internallumen 52 of the obturator 50 is longer in axial length than the largediameter internal lumen 22 of the introducer cylinder 20; and that thecutout slot 40 of the introducer cylinder 20 exposes the obturatordistal end 62 to the ambient environment at the composite distal end 72.Moreover, the portal 64 of the obturator 50 passes through the planarsurface 38 of the introducer cylinder 20 and extends into the ambientenvironment with the concurrent exposure of the distal tapered end tip62 and the portal 64 beyond the composite distal end 72.

The cylinder-obturator composite of FIG. 6 is the article to bepercutaneously introduced into a peripheral vein and is to be extendedintravenously through the peripheral vein until a desired location isreached. The percutaneous introduction is achieved typically bypositioning a guidewire in the desired vein, utilizing percutaneousvenipuncture, guiding catheters, fluoroscopy, and contrast venography.The back of the guidewire is first passed through the portal 64 at thedistal end tip 62 and then passed through the internal lumen 52. Theentire cylinder-obturator composite is then extended over the guidewireinto the vein. The guidewire introduced at the portal 64 will travelover the entire axial length of the internal lumen of the obturator andexit at the composite proximal end 70 in a conventionally known manner.The cylinder-obturator composite is then extended intravascularly usingthe guidewire as the means for extension through the vein. In thismanner, the obturator acts as a support vehicle and stiffening rod forthe venous catheter during initial introduction and placement of thecatheter in the vein.

When a vascular site is chosen which is deemed suitable for use, theentirety of the obturator 50 is removed from the internal lumen 22 ofthe introducer cylinder 20. The obturator of FIG. 5 is then to beentirely replaced and be substituted for by the tubular cutting toolillustrated by FIGS. 7 and 8 respectively. FIG. 7 shows the entirety ofthe tubular cutting tool as configured for this preferred firstembodiment; and FIG. 8 shows particular details and individualstructures existing at the distal end of the cutting tool.

As shown in FIG. 7, the tubular cutting tool 80 is an extended hollowtube 82 whose external diameter is sized to be only slightly smallerthan the internal lumen diameter 22 for the introducer cylinder 20 ofFIG. 4. The tubular cutting tool 80 itself has a small bore internallumen 84 whose volume provides several capabilities. In part, theinternal lumen 84 serves as a communication passageway for carrying anactuation wire 86 which is inserted at the proximal end 88 and conveyedvia the internal lumen 84 to the distal end 94 of the cutting tool 80.The actuation wire 86 is employed by the physician to activate thevascular wall perforation capability on-demand. In addition, theinternal lumen 84 serves as a volumetric passageway for the conveyanceof pressurized carbon dioxide gas from the proximal end 88 to the distalend 94. A gas conduit 85 is attached to and lies in fluid flowcontinuity with the internal lumen 84 at the proximal end 88. A sourceof pressurized carbon dioxide gas (not shown) is controlled by astopcock 87 which introduces a flow of pressurized carbon dioxide gas atwill into the volume of the internal lumen 84 for conveyance to thedistal end 94. An aperture 97 in the tubular cutting tool 80 at thedistal end 94 provides for egress of the pressurized carbon dioxide gasafter being conveyed through the internal volume 84.

Note also that the proximal end 88 is configured as an oval disc 90having a rib 92 extending therefrom. The proximal end 88 thus forms partof an interlocking system suitable for engagement with the lockingarrangement 26 of the introducer cylinder 20 illustrated previously byFIG. 4 herein. The radiopaque components of the cutting tool arenon-axisymmetric which allows the polar (rotational) orientation of thecutting tool-introducer cylinder composite to be determinedfluoroscopically. The cutting tool-introducer cylinder composite canthen be rotated by manipulating the proximal end to adjust polarorientation.

FIG. 8 (as a cutaway view) reveals the details of the distal end 94 ofthe tubular cutting tool 80. The distal end 94 has three specific parts:a tapered end tip 96; vascular wall perforation means 98; and first andsecond magnet means 100a and 100b positioned adjacent to and in axialalignment with the vascular wall perforation means. It will berecognized and appreciated that (as shown within FIG. 8) the vascularwall perforation means 98 is situated near the tapered end tip 96 and isflanked by first and second magnet means 100a and 100b. However, theplacement and ordered sequence of the magnet means 100a and 100b and thevascular wall perforation means 98 can be altered and interchanged inlocation as acceptable variations to the ordered sequence of partspresented by FIG. 8. Furthermore, a single magnet means rather than useof a pair is acceptable as another variation of the construction andstructure.

In addition, it will be seen that the actuation wire 86 extends from theproximal end through the lumen 84 to the distal end 94 and connects withthe vascular wall perforation means 98 such that the perforationmechanism can be activated at will and on-demand by the physicianretaining possession of the proximal end of the tubular cutting tool 80which remains exposed to the ambient environment outside the skin.

FIG. 8 also reveals several notable features about the magnet means 100aand 100b and the vascular wall perforation means 98 respectively. Themagnet means are housed within and contained by the tubular wall of thecutting tool 80 entirely. The magnet means are desirably rare earthmagnets or electromagnets having sufficient magnetic power and strengthto attract and align another source of magnetic attraction such as asecond catheter with the magnetic properties in-vivo. The magnet meansmay be a solid rod or a configured bar of matter within the lumen of orintegral to the tubular wall of the cutting tool. While the actualdimensions may vary widely and radically, a typical rare earth magnetwill be configured as a cylindrical mass 8-10 mm in length and 2-3 mm indiameter. The magnetic means are firmly embedded within the interior ofthe tubular cutting tool and will not shift or change position ororientation after the tubular cutting tool 80 has been manufactured andcompletely assembled.

Note also that the vascular wall perforation means of FIG. 8 restscompletely within the interior volume of the cutting tool in the passivestate but is elevated to become exposed to the ambient environment inthe activated state. As is shown within FIG. 8, a fenestration 112permits ambient exposure of a perforating mechanism through the tubularwall of the cutting tool 80 via elevation onto a tracked template 110which escalates the perforation mechanism to a greater height fromwithin the interior of the cutting tool 80. The particular perforationmechanism illustrated within FIG. 8 is shown as a sliding electrode 114through which radiofrequency cutting current is passed.

The means by which the perforation mechanism is activated and placed inappropriate elevated position to achieve perforation is shown by FIGS.9A-9D respectively. The actuation wire 86 provides the physician withthe point of control. As the actuation wire 86 is pulled by theattending physician at the proximal end, the sliding electrode 114 iselevated and moves along a set track on the template 110. The non-lineargeometry of the track causes the electrode 114 to protrude through thefenestration 112 and become exposed to the ambient environment over theentire length of the template distance. Subsequently, when the actuationwire is advanced towards the distal end, the electrode 114 travels inthe reverse direction and returns to its original position within theinterior of the tubular cutting tool 80. In this manner, the attendingphysician can activate and inactivate the perforation means at will; andcause the sliding electrode 114 to become exposed as a consequence ofmoving along a set track and distance; and then to subsequently withdrawand reverse its direction of travel such that it becomes enclosed againand protected by the tubular wall of the cutting tool 80.

During the activation of the sliding electrode 114, a radiofrequencyalternating current of predetermined amplitude (a) and frequency (f) isapplied to the electrode and conducted through actuation wire 86 with acomplimentary electrode disposed within the arterial catheter serving asthe ground. The radiofrequency current traveling from the elevatedelectrode 114 in the tubular cutting tool 80 to the complimentaryelectrode in the arterial catheter thus is the active cutting forcewhich creates a perforation through the vascular walls on-demand. Toprovide sufficient and readily available radiofrequency current when andas required, a conventional electrosurgical console (such as a BOVIE,BARD, or VALLYLAB console) is preferably used as a power source.

Concurrent with electrode activation, the attending physician will alsoopen the stopcock 87 and allow a flow of compressed carbon dioxide gas(CO₂) into the tubular cutting tool 80. Preferably an electricallyactuated solinoid (not shown) is used to release a burst of compressedCO₂ gas from the pressurized tank in synchrony with the application ofthe radiofrequency current. The released burst of the compressed CO₂ isdelivered through the gas conduit 85 into the internal lumen 84, whereit travels through the interior of the cutting tool 80 to the aperture97, and exits through the aperture 97 into the vein lumen. The volume ofCO₂ gas exiting the aperture 97 transiently displaces the venous bloodin the area of the fenestration 112 during the radiofrequency activationof the sliding electrode 114, a highly advantageous circumstance. Bloodis an aqueous, electrolyte-rich fluid which conducts electrical currentreadily. As such, the temporary displacement of blood by CO₂ in the veinlumen (and after perforation in the arterial lumen as well) at theselected anatomic site is desirable to obtain sufficient electricalcurrent density at the point of electrode contact to cleanly incise andpenetrate through the vascular walls.

The complete venous catheter suitable for activation on-demand and forgenerating an AV fistula is shown by FIG. 10. Clearly, the insertion ofthe tubular cutting tool 80 into the internal lumen 22 of the externalcylinder 20 in a locked arrangement provides the venous cathetersuitable for use in-vivo. The cylinder-cutting tool composite of FIG. 10is the complement and counterpart of the cylinder-obturator composite ofFIG. 6. However, the functions of each composite construction aremarkedly different. Thus, whereas the cylinder-obturator composite ofFIG. 6 provides a highly desirable catheter for percutaneousintroduction and extension intravenously through a peripheral vein to aspecific location or chosen anatomic site, the cylinder-cutting toolcomposite of FIG. 10 provides the alignment and specific placementintravenously at a chosen anatomic site within the vein as well asproviding the physical mechanism and means by which to perforate thevascular walls of closely associated veins and arteries concurrently. Inaddition, the radiopaque non-axisymmetric components allow fluoroscopicidentification and manual adjustment of polar (rotational) orientationof the cutting tool-introducer cylinder composite.

The construction and organization of the arterial catheter

The arterial catheter is a long, flexible hollow tube having a fixedaxial length, a discrete proximal end, a discrete distal end, and atleast one internal lumen of predetermined volume as is illustrated byFIG. 3 herein. Typically, the axial length will vary in the range fromabout 40-150 centimeters and the external diameter of the hollow tubewill often be in the range from about 1.5-2.5 millimeters in size. Whilethe proximal end of the arterial catheter is conventional in mostrespects, the internal lumen of the catheter is preferably joined to andlies in fluid communication with a source of compressed carbon dioxidegas (CO₂) in a manner similar to that previously described herein forthe proximal end of the venous catheter. Thus, compressed CO₂ gas isreleased on-demand from a pressurized tank; is delivered via a gasconduit into the internal lumen; and travels through the linear volumeof the internal lumen to a distal aperture through which the CO₂ gasexits into the arterial lumen in-vivo. The volume of CO₂ gas exiting thecatheter displaces at least some of the arterial blood in the anatomicarea of the electrode; and maintains the radiofrequency electricalcurrent density at the point of contact between the radio frequencyelectrode and the vascular tissue. This will facilitate clean incisionof the vascular walls.

The distal end of the arterial catheter is unique in structure,construction, and organization. A detailed showing of the distal end isprovided by FIG. 11. As shown by FIG. 11, the arterial catheter 200 hasa distal end 212 which is divided into four individual segments inseries. Farthermost is the tapered distal end tip 224 having portals 226and 210 and non-axisymmetral lumen 227 for externalized passage of aguidewire there through; and an aperture 234 for the egress ofcompressed CO₂ gas into the arterial lumen. The tapered distal end tip224, the portals 226 and 210, and the lumen 227 thus serve as and areadapted for intraarterial guidance of the arterial catheter externallyover a guidewire and through a blood vessel in-vivo to a chosen anatomicsite. In contrast, the aperture 234 is in direct communication with theaxial internal lumen 214 and allows the passage of compressed CO₂ gasthrough the catheter interior with egress via the aperture. Thisfacilitates the creation of the AV fistula by displacement of arterialblood on-demand at the chosen anatomic site.

Positioned adjacent to the tapered distal end tip 224 are a pair of rareearth magnets 228a and 228b which serve as the magnet means for thisembodiment. The rare earth magnet pair 228 is set in axial alignmentwith the distal end tip 224 and has sufficient magnetic power andstrength to cause an adjustment in intraarterial catheter position whenplaced in proximity with the magnet means of the venous catheterdescribed previously herein.

The fourth structure is the fixed electrode 230 which serves as theelectrical ground for the radiofrequency circuit; and which ispositioned adjacent to and flanked by the rare earth magnet pair 228 andwhich is set in axial alignment with the tapered distal end tip 224 ofthe arterial catheter 200. The arterial electrode 230 providesintravascular support for a chosen portion of the arterial wall andcompletes the radiofrequency circuit during the perforation processin-vivo in order to generate an AV fistula. The remainder of the hollowtubular wall 202 and the axial internal lumen 214 are as previouslydescribed.

Since magnetic interaction is deemed essential to the proper function ofthe arterial catheter, the magnetic means preferred in this embodimentis the use of two rare earth magnets which will provide sufficientmagnetic power to cause an intravascular adjustment in position for thearterial catheter when in proximity to the magnetic means of the venouscatheter in-vivo. Desirable magnetic materials for use as magnet meansthus include the neodymiun-iron-boron compositions and cobalt-samariumcompositions. Alternatively, an electromagnet can be substituted inplace of a rare earth magnet composition as a desirable magnetic means.In addition, any other source of magnetism which can be demonstrated toprovide sufficient magnetic power (as conventionally measured anddetermined in Gauss) may be employed and positioned as an effective anduseful substitute.

In comparison, the arterial electrode has two specific functionsin-vivo: To provide a physical source of reinforcement and supportduring the process of perforating both the venous and arterial vascularwalls concurrently; and to provide a grounding terminal for completionof the radiofrequency electrical circuit. The electrode may therefore becomposed of any non-ferrous conductive matter such as carbon, copper,zinc, aluminum, silver, gold, or platinum.

Alternative catheter embodiments and formats

In the preferred embodiment of the catheter apparatus, both the venouscatheter and the arterial catheter comprise electrodes; and the activeforce for transvascular perforation of the closely associated vein andartery at a chosen anatomic site is via the transmission of aradiofrequency electrical current at a predetermined amperage andfrequency from the electrode embedded in the aligned venous catheterthrough both vascular walls to the grounding electrode within thealigned arterial catheter. The use of radiofrequency electric current,however, is only one means for perforating the vascular walls of aclosely associated vein and artery in order to generate an AV fistulain-vivo.

In an alternative embodiment of the vascular wall performation meansdisclosed in detail hereinafter, a static discharge electrical spark isused to perforate the vascular walls between the electrode in the venouscatheter and the electrode in the arterial catheter. The electrodes inthis alternative format would differ little in design and structure fromthose depicted in the preferred embodiment. Moreover, the displacementof venous (and arterial) blood by the introduction and subsequentrelease of compressed CO₂ gas through the catheter internal lumen inthis alternative embodiment would also desirably occur as described forthe preferred embodiment previously herein; but this usage and featureis optional and is not a necessary adjunct to the process of vascularwall perforation and AV fistula formation created by the use of a staticelectrical spark between the electrodes.

In still another embodiment of a useful catheter construction, thevascular wall perforation means can take form as a microscalpel ofconventional design which may be elevated from and subsequently recessedback into the internal volume of the tubular cutting tool at the distalend using the fenestration and the tracked template of the venouscatheter described previously for the preferred embodiment. Themicroscalpel is used mechanically to incise and bore into the vascularwalls without the aid of electrical current. The venous cutting tool isstructurally similar to that disclosed as the preferred embodiment withthe exception that the sliding electrode has been replaced by a slidingmicroscalpel, which is similarly activated on-demand by the physicianusing the actuation wire. In this microscalpel embodiment, however, thepresence of compressed CO₂ gas at the anatomic site chosen for AVfistula formation has no advantage; consequently, the gas conduit, thestopcock, and the source of pressurized CO₂ gas as components of thevenous catheter are unnecessary and redundant. Furthermore, in thismicroscalpel construction format, the electrode disposed at the distalend of the arterial catheter in the preferred embodiment is now replacedand substituted by an abutment block (or anvil) segment which ispositioned adjacent to and is flanked by at least one or a pair of rareearth magnets for catheter alignment as previously described. Theplacement and orientation of the abutment block is similar to that shownfor the grounding electrode in the preferred arterial catheterconstruction; but the abutment block is typically a cylinder or rodcomposed of hard and generally nonconductive, resilient matter whichwill provide firm support during the vascular wall perforation process;and also serve to confine the microscalpel cutting action to penetratingonly a small and limited area of arterial vascular wall at the chosenanatomic site--thereby preventing excessive vascular injury. The rangeof resilient materials suitable for the abutment block thus include hardrubbers, plastics such as LEXAN or PLEXIGLASS polymers, polycarbonatecompounds, vinyl polymers, polyurethanes, or silicon-based compositions.

The functional relationship between the venous catheter and the arterialcatheter

Both the venous catheter and the arterial catheter comprise uniquefeatures at their respective distal ends which will provide properalignment in-vivo in order that a AV fistula can be generated on demand.Clearly, it is envisioned and intended that the venous catheter will bepercutaneously introduced and extended through a peripheral vein until adesirable anatomic location is reached. Similarly, it is expected thatthe arterial catheter will be percutaneously introduced into andextended through a closely associated peripheral artery until both thearterial catheter and the venous catheter lie in adjacent position, eachwithin its own individual blood vessel. A representation of thisadjacent positioning between the preferred arterial catheter and thevenous preferred catheter is illustrated by FIG. 12.

As shown within FIG. 12, each of the preferred catheters individuallywill rest intravascularly within its own blood vessel (which has beendeleted from the figure for purposes of clarity) and lie in parallelalignment as a consequence of the magnetic attraction between the pairof rare earth magnets 228a and 228b of the arterial catheter 200 and theopposite pair of rare earth magnets 100a and 100b of the venous catheter10. The magnetic attraction between these four rare earth magnets is ofsufficient magnetic power to cause intravascular adjustment in positionfor the venous catheter 10 and the arterial catheter 200 lying withintheir individual, but immediately adjacent, blood vessels. The magneticattraction and force is thus a transvascular effect and result wherebythe magnetic field affects each of the catheters lying individually andseparately in different but closely associated blood vessels.

It is also important to note the orientation effect and overallalignment pattern created as a consequence of transvascular magneticattraction. The venous catheter is shown as extending in a easternlydirection such that the perforation means 98 (including the slidingelectrode 114, the elevating template 110 and the fenestration 112) arein proper position and flanked by the pair of the rare earth magnets100a and 100b. In comparison, the arterial catheter 200 lies in anwesternly direction such that the arterial catheter body is brought intoaligned position over the distal end tip 96 of the venous catheter 10;and consequently, that the grounding electrode 230 of the arterialcatheter 200 is brought directly into generally parallel alignment withthe vascular wall perforation means 98 of the venous catheter 10. Inthis manner, the grounding electrode 230 of the catheter then lyingwithin the peripheral artery becomes closely associated and in properalignment with the sliding electrode 114 of the venous catheter 10 thenlying with the peripheral vein. The only intervening matter existingin-vivo is thus the thickness of the peripheral vein wall, the thicknessof tissue between the closely associated vein and artery, and thethickness of the arterial wall itself. In correctly chosen anatomicsites, the sum of these three thickness layers will typically be lessthan 3 mm in total distance. The sliding electrode (or other vascularwall perforation means) can then be activated on-demand and at will withsubstantial certainty that the physical action of perforating both thevenous and arterial vascular walls can be achieved with minimal injuryto the blood vessels and with a minimal loss of blood volume into thesurrounding tissues.

It is essential to recognize and appreciate, therefore, that it is themagnetic attraction between the rare earth magnets positioned in advanceand set in axial alignment within each of the venous and arterialcatheters individually which creates the phenomena of transvascularmagnetic attraction and interaction and which generates sufficient forcesuch that the individual catheters lying in adjacent blood vessels willmove in axial position as a consequence of the strength of the magneticinteraction. Moreover, each catheter will move more readily with itsrespective vessel lumen to apply compressive force; and in so doing,minimize the distance between the radio frequency electrode and thesliding electrode. The grounding electrode of the arterial catheter andthe sliding electrode of the venous catheter are similarly aligned andset in advance within each of the respective catheters such that whenthe transvascular magnetic attraction occurs and each of the cathetersindividually move into position as a consequence of magnetic attraction,the vascular wall perforation means will then be in proper parallelalignment to generate an AV fistula on demand in a safe and reliablemanner.

B. An Alternative Embodiment of the Catheter Apparatus

An alternative embodiment of the present invention provides a pair ofcatheters which are used in tandem for generating an AV fistulaon-demand between a closely associated artery and vein at a chosenvascular site in-vivo. Each of the individual catheters constituting thepair are structurally similar except for a few detailed features.

For purposes of description and detail, a single catheter of the pairwill suffice. Accordingly, all which pertains to the description of onecatheter applies completely to the construction, structure, and featuresof the other catheter constituting the pair. Each catheter comprises onehollow tubular wall having a fixed axial length, a discrete proximal endof conventional manufacture and design, a unique discrete distal end,and provides two internal lumens (of unequal diameter and predeterminedsize) which extend coaxially and substantially in parallel over theaxial length of the tubular wall. Since the structural features ofdistinction exist primarily at the distal end of each catheter, thisdetailed disclosure will focus and emphasize these unique structures andfeatures.

The distal end of the dual lumen catheter intended to be used in pairsfor generating an AV fistula are illustrated by FIGS. 13, 14, and 15respectively. FIG. 13 provides an overhead view of the catheter at thedistal end; in comparison, FIG. 14 provides an axial-section view of thecatheter distal end while FIG. 15 provides a cross-sectional view of thecatheter taken along the axis Y Y'.

As shown by FIGS. 13-15, each of the catheters 300 comprises a tubularwall 302 which terminates at the distal end 304 as an end tip 306adapted for passage of a guide wire and for intravascular guidance viaportals 305 and 309 and non-axisymmetric lumen 307 through a bloodvessel in-vivo to a chosen vascular site. Within the tubular wall 302are two internal lumens 308, 310. The first internal lumen 308 extendsfrom the proximal end of the catheter (not shown) and terminates at thedistal end 304 as a portal 312. The diameter of this first internallumen 308 is relatively large; and this first internal lumen is intendedto carry a variety of fluids such as liquid contrast medium forradiological purposes and pressurized gases as CO₂ for displacing bloodat the chosen anatomic site. The second internal lumen 310 extends fromthe proximal end of the catheter (not shown) as a relatively small boretube and terminates at the distal end tip 306 where a fixed electrode320 is imbedded. The second internal lumen 310 thus serves as theconduit for an electrical lead 322 which is carried from the proximalend of the catheter through the catheter mass via the second internallumen 310 and ends at the distal end tip 306 at the embedded electrode320.

Note that the fixed electrode 320 is joined to the electrical lead 322which is in electrical communication with a source of electrical energy(not shown) capable of producing a static electrical charge on command.The electrode 320 is typically formed of solid, electrically conductivemetal. The electrode 320 comprises at least two component parts: anelectrical supporting unit 324 which is embedded in the material of thecatheter wall and firmly fixed in position within the catheter mass; andan extending discharge spike 326 which extends from the support unit 324through the thickness of the catheter wall material and terminates inthe ambient environment. As an electrical system, a static dischargefrom the electrical source is introduced through the catheter via theelectrical lead 322 and conveyed to the electrode 320 on demand. Theelectrical current is conveyed to the supporting unit 324 and the chargeis then discharged through the spike 326 from the interior of thecatheter into the external ambient environment as a static electricalspark of predetermined magnitude.

Positioned adjacent to the electrode 320 and set in fixed alignment atthe distal end tip 306 is a rare earth magnet 330 (or, alternatively,other magnet means). This rare earth magnet is configured desirably as arectangular block of magnetic metal formed of neodymium-iron-boron alloyand/or cobalt-samarium alloy. Note also that the orientation of themagnetic attraction in terms of the "north" and "south" polarity isknown and identifiable. The rare earth magnet thus serves as magnetmeans positioned at the distal end and set in axial alignment at thedistal tip of the catheter. In addition, an optional second rare earthmagnet 332 may be set in fixed alignment to flank the electrode 320. Theoptional second rare earth magnet 332 is desirably identical inconfiguration and composition to the magnet 330; and provide addedmagnetic force for alignment. These magnet means have sufficientattractive force to cause an adjustment in position for the catheterin-vivo when placed in proximity with another source of magneticattraction disposed within a closely associated (and preferablyadjacently positioned) blood vessel.

In comparison it will be recognized that the electrical lead 322, theelectrode 320, the supporting unit 324 and the discharge spike 326collectively constitute the vascular wall perforation means for thisembodiment. Note that the entire electrical current carrying and spikedischarge apparatus constituting the vascular wall perforation means arepositioned adjacent to at least one rare earth magnet (the magnet means)of the catheter and are set in axial alignment with the distal end tipof the catheter. Thus, when there is a magnetic interaction involvingthe rare earth magnet 330 (and optionally the rare earth magnet 332),this static electrical system will become intravascularly adjusted inposition in-vivo; and the static discharge will serve as the means forperforating the vascular walls at will whenever sufficient potential isapplied to the two electrodes to generate an AV fistula.

The intended manner of usage under in-vivo conditions is illustrated byFIG. 16. For purposes of clarity the first catheter 300a is presumed tobe in a peripheral vein whereas the second catheter of the pair 300b isenvisioned as being within a peripheral artery. The vascular walls havebeen deleted from the figure to demonstrate the working relationshipbetween the two catheters in tandem and the mechanism by which an AVfistula is generated using this catheter apparatus.

As shown by FIG. 16, the only difference between the first catheter 300aand the second catheter 300b is the polarity and polar orientation ofthe rare earth magnets 330a, 330b (and optionally rare earth magnets332a, 332b). Recalling also that each catheter has been placed withinthe confines of an individual blood vessel constituting a closelyassociated peripheral artery and vein, it is clear that the oppositepolarity in each rare earth magnet will attract the catheters towardseach other. Thus, a transvascular magnetic attraction occurs which notonly moves each of the catheters 300a, 300b individually within its ownblood vessel in a manner which brings the pair closely together, butalso the strength of the magnetic attraction is sufficiently great inpower (Gauss) that the rare earth magnets are drawn and aligned to eachother in parallel positions as shown within FIG. 16. The consequence ofthis transvascular magnetic attraction and alignment in parallel betweenindividual catheters disposed in separate blood vessels independentlycauses the electrodes 320a, 320b and the discharge spikes 326a, 326b tobecome closely placed and aligned in parallel. It is also desirable inpractice to ascertain that adequate alignment by magnetic attraction hasoccurred and that a suitably small distance occurs between theindividual discharge spikes by measuring the electrical resistancebetween the electrical contacts 320a, 320b. Fluoroscopy confirmsappropriate catheter position, alignment, and polar (rotational)orientation.

After the determination of adequate alignment is made, the source ofstatic electrical discharge is engaged, and the electrical charge isconveyed to the electrode discharge spikes. A static electrical chargeis accumulated, discharged and passed from one of the spikes 326a to theother aligned spike 326b, thereby completing the electrical circuit. Inso completing this electrical circuit, the electrical spark vaporizesportions of the vascular wall for both the vein and the artery at thesame moment. The arcing spark vaporizes vascular tissue and creates aperforation in common between the blood vessels. Blood in the arteryrushes through the perforation in the arterial wall into the alignedhole of the perforation in the vascular wall of the adjacentlypositioned vein. In this manner, the AV fistula is generated safely,reliably, and on-demand.

It will be noted and appreciated that this alternative embodiment of thecatheter apparatus can also employ other vascular wall perforation meansthan a static electrical discharge to perforate the vascular wall. Animmediate and easily available substitution and replacement for theentire electrical lead, electrode, and discharge spike--the perforationmeans--is the use of a fiber optic cable and a source of laser (light)energy. The fiber optic cable (comprised of multiple fiber opticstrands) is conveyed through the internal lumen and passes through thetubular wall material of the catheter at the distal end tip to terminateas a fiber optic end surface exposed to the ambient environment. Thefiber optic cable would then transmit and convey laser (light) energyfrom the energy source on-demand as the means for perforating thevascular wall of the closely associated blood vessels. Also, thecatheter lying in the adjacent blood vessel would serve to diffuse theapplied laser energy and prevent injury to the opposite vascular wall.

V. An Illustrative Method for Creating an AV Fistula In-Vivo Using thePreferred Embodiment

To demonstrate the methodology employing a catheter apparatus togenerate an AV fistula between a peripheral artery and an adjacent vein,it is desirable to focus upon and utilize a specific anatomical area inthe extremities of a living patient as an illustrative example. For thisillustrative purpose alone, the description presented hereinafter willemphasize and be limited to the creation of an AV fistula between theradial or ulnar arteries and a closely associated and adjacentlypositioned vein in the distal forearm. It will be expressly understoodand recognized, however, that this illustrative description is merelyrepresentative of such procedures generally; and is but one example ofthe many different and diverse instances of use which can be reproducedin many other anatomical areas of the body at will and on-demand. Underno circumstances, therefore, is the present invention and methodology tobe or restricted to the particular anatomic sites described or limitedto the particular embodiment of the catheter apparatus employed.

The illustrative example presented below employs the preferredembodiment of the catheter apparatus described in detail previouslyherein. Clearly, although this preferred embodiment is deemed to be anadvantageous construction and the best mode structure developed to date,all other alternative embodiments of the catheter apparatus--regardlessif used singly or in pairs--are also deemed to be suitable andappropriate for use in a manner similar to that described below. Inaddition, given the wide range and diversity of structural components,design features and format variations in catheter construction whichhave already been disclosed herein and are within the scope and breadthof the present invention, it will be understood that certain minorchanges in the procedural details and modes of use may be necessarywhich differ from the preferred methodology.

Initially, and most importantly, it will be recognized and appreciatedthat the methodology is intended to be performed in the angiographysuite of a hospital by thoroughly trained and experienced invasiveradiologists. The reader is presumed to be familiar with the commonprocedures performed by invasive radiologists today; and no attempt willbe made herein to familiarize or acquaint the reader with theconventional techniques of ultrasound imaging, fluoroscopy andfluoroscopic imaging, and other radiological techniques for contrastimaging. The reader is also presumed to be familiar with generalprocedures of catheterization and especially with the modified Seldingertechnique reviewed in detail previously herein. Finally, to aid thereader in becoming acquainted with the essence of the methodology and inorder to appreciate its importance and major advantages, FIGS. 17-26 areincluded; and direct reference and comparison of these figures will aidin ease of understanding and full comprehension of the methodologicaldetails.

The first step in the methodology involves obtaining percutaneousarterial access to a suitable peripheral artery (such as the radial orulnar arteries) in the forearm through the brachial artery or, lessdesirably, the common femoral artery. An introducer sheath is placedinto the brachial artery using conventional techniques describedextensively in the medical literature. The sheath is placed at mid-bicepand directed distally towards the hand. An intravascular ultrasoundprobe (hereinafter "IVU") is then introduced over a guidewire into theforearm arterial blood vessels. This is shown by FIG. 17 which shows theintravascular ultrasound probe being passed antegrade into the radialartery.

The IVU provides circumferential ultrasonic visualization of structuresin the immediate vicinity of the artery in which it is positioned as isillustrated by FIG. 18. As shown, FIG. 18 clearly demonstrates two largeveins ("V") immediately adjacent to the radial artery ("A") at theposition shown by FIG. 17. Veins in the forearm that lie in closeproximity to the radial artery are readily identified. The echolucentblood in the veins stands out in sharp contrast to the relativelyechogenic fibrous and fatty tissues and muscle which surrounds the veinsthemselves. Desirably, the IVU is passed through both the radial andulnar arteries independently and in succession in order to note thelocation and position of those large diameter veins lying immediatelyadjacent to the artery. Commonly, several anatomical zones are presentin the forearm of most patients where large diameter veins pass withinone or two millimeters of these major peripheral arteries. From amongthese anatomical zones, one of these is selected for the generation ofthe AV fistula. Ideally, the chosen anatomical area should be fairlydistal or peripheral in the forearm, as this will result in a greaternumber of veins being exposed to high volume flow and thus a greaternumber of potential access sites for percutaneous venipuncture. Becauseveins have unidirectional valves in them, veins distal to the AV fistulawill not generally dilate.

This result is illustrated by FIG. 19 where the anatomic area isselected in the distal radial artery in the location where a sizablediameter vein lies immediately adjacent to the arterial wall. The chosenanatomic site is shown by the intravascular, ultrasound image of FIG. 20which reveals an adjacently positioned vein on one side of the radialartery lumen.

The second step is to obtain venous access for the venous catheter whichtakes form initially as the cylinder-obturator composite describedpreviously herein. Percutaneous venous access is desirably obtained atthe wrist. Fluoroscopic contrast venography is performed to defineforearm venous anatomy. Under fluoroscopic guidance, a radiologicalguide wire is advanced through the percutaneous venous access to thechosen vein at the anatomic zone selected for generating the AV fistulain the forearm. The techniques required for this maneuver areconventional and fundamental to the practice of invasive radiology. Thisprocedure is illustrated by FIGS. 21 and 22 respectively. Fluoroscopyshows the guidewire to be in close proximity to the IVU probe. Inaddition, as shown by FIG. 22, the extremely echogenic guidewire iseasily visualized and imaged within the chosen vein lumen by IVUimaging. In this manner, the proper placement of the venous catheter inthe chosen vein is inserted.

As shown by FIG. 21, the preferred venous cylinder-obturator composite10 is introduced at the wrist and passed antegrade into the chosen veinover the previously placed guidewire. Fluoroscopy and intravenouscontrast medium assist extension and guidance of the venous catheterthrough the vein; and a correct position is identified and placementconfirmed for the venous catheter at the chosen site in the vein. Onceagain, IVU readily demonstrates the venous catheter within the lumen ofa chosen vein.

It will be recalled that the venous catheter (the introducercylinder-obturator composite format) measures 6-9 French (approximately2-3 mm) in diameter; and typically will be about 40 centimeters inlength. At the proximal end, the radiologist uses a handle to manipulatethe venous catheter during placement. The venous catheter desirablyemploys the removable solid obturator during this phase in order tofacilitate advancement of the venous catheter complex, preferably asdescribed previously, the obturator has about a 0.2-0.5 mm internallumen which extends coaxially down its central axis and allows thevenous catheter complex to be passed coaxially over the guidewire intothe proper position after the guidewire placement has been verified ascorrect.

Once good positioning and placement is verified and confirmed for thevenous catheter (the introducer cylinder-obturator composite format),the IVU probe is removed and replaced with the arterial catheter 200described previously herein. The construction of the arterial catheterprovides substantial flexibility and offers a much longer axial lengththan its venous counterpart. Typically, the arterial catheter has anexternal diameter of about 5-7 French (approximately 1.5-2 mm indiameter) and has a typical length of about 100 centimeters tofacilitate placement in an accessible artery. However, passing thepositioned guidewire internally through the entire 100 cm length ofcatheter can be cumbersome and difficult. For this reason, the arterialcatheter (much like the IVU probe) typically has a short-length,non-axisymmetric passageway or lumen which extends from the center ofthe distal end tip tangentially for about 1 cm distance and ends at thesidewall of the catheter about 1 centimeter from the distal end. Thisshort non-axisymmetric lumen provides an externalized "monorail" mode ofpassage for the guidewire after insertion at the distal end tip; andallows the arterial catheter to be passed over the properly positionguidewire without need for internally passing the guidewire through theentire axial length of the catheter. This "monorail" mode ofexternalized guidewire passage through a catheter is conventionallyknown, facilitates proper placement, and offers better control of thecatheter for the radiologist when positioning the arterial catheterin-vivo.

The manipulation and introduction of the arterial catheter isillustrated by FIGS. 23 and 24 respectively. As shown by FIG. 23, afterthe intravascular ultrasound probe has been removed, the arterialcatheter is passed over the previously positioned guidewire, introducedinto the artery, and advanced to the chosen anatomical site previouslyheld by the IVU probe, Moreover, as illustrated by FIG. 24, fluoroscopyreveals when good and proper alignment exists between the positioningsof the arterial catheter in relation to the venous catheter in theclosely associated vein. Thus, under the fluoroscopic guidance, thearterial catheter is advanced over the guidewire into the radial arteryto the chosen position previously occupied by the IVU probe.

After ascertaining that close proximity of the arterial catheter to thevenous catheter exists, the relative positions are carefully adjustedunder fluoroscopy such that the radiopaque markers on each of thecatheters are carefully in alignment. In addition, radial radiopaquemarkers on the introducer cylinder allow rotational position to beadjusted fluoroscopically to insure correct orientation of the distalfenestration. Thus, when correctly aligned, the two catheters (eachwithin its individual blood vessel) will overlap for an estimateddistance of about 35 mm. If the overlapping distance does not appear tobe adequate or if the radiologist is unsure that the two catheter tipsare properly aligned, each of the catheters may be adjusted in positionas long as needed in order to verify and confirm a proper alignment.

When, and only when, a correct and proper alignment has been madebetween the arterial and venous catheters in-vivo, the obturatorcomponent is removed from the venous introducer cylinder and replacedwith the tubular cutting tool previously described. The tubular cuttingtool is a semi-rigid rod with the same dimensions as the obturator andcomprises the pair of rare earth magnets having the proper size andorientation to attract the rare earth magnets within the arterialcatheter distal end. The magnetic attractive force will cause atransvascular attraction between the two opposing pairs of rare earthmagnets; and the magnetic attractive force is of sufficient magnitudesuch that the arterial catheter and the venous catheter will adjust inposition individually as a result and consequence of the magneticinteraction. This event and effect is illustrated by FIG. 25 in whichthe arterial catheter lying within the radial artery moves into properalignment and precise positioning as a result of the magneticinteraction with the magnet means of the venous catheter lying withinthe adjacent vein. After this transvascular magnetic attraction andadjustment in position between the two catheters has occurred, thevascular wall perforation means at the distal end of the venous cathetermay be activated at will and on-demand to generate the AV fistula atthat precise location.

The preferred embodiment of the venous catheter 10 employed utilizes aradiofrequency electrode which slides in a controlled track upon aelevating template and which becomes exposed through a fenestration as aresult of traveling over the template track. The sliding electrode isactuated by way of a sliding wire running the length of the tubularcutting tool; and the actuation wire is engaged preferably by a screwmechanism in the handle at the proximal end held by the radiologist.Once actuated, the electrode is moved along the curvilinear track on theelevating template resulting in the protrusion of the electrode throughthe fenestration into the exterior of the venous catheter.Simultaneously, radiofrequency current is delivered to the slidingelectrode by way of the conductive actuation wire; and the groundingelectrode in the arterial catheter completes the electrical circuit forvascular perforation to proceed. The degree of electrode protrusion fromthe venous catheter is such that the sliding electrode impinges on thematerial of the grounding electrode of the arterial catheter which is inaligned parallel position directly adjacent to the venous catheter. Thiscircumstance is illustrated by FIG. 26.

In this manner, the protruding sliding electrode of the venous cathetercan be moved up to 8 mm axially depending on the desired length of theincision; and the grounding electrode of the arterial catheter completesthe radiofrequency electrical circuit (as shown by FIG. 26). Bycompleting the radiofrequency electrical circuit at the chosen anatomicsite and delivering the appropriate current to the completed circuit, adirect and effective perforation of the venous vascular wall and thearterial vascular wall concurrently can be achieved on-demand.

Simultaneous with the delivery of radiofrequency electrical energy tothe completed circuit, a bolus of compressed carbon dioxide gas isintroduced into the lumens of both the artery and the immediatelyadjacent vein. The CO₂ gas transiently displaces the blood at the chosenanatomic site during the process of perforating both vascular walls.Since blood is an electrically conductive medium, the CO₂ gasdisplacement increases the current density at the point of contactbetween the radiofrequency electrode and the vascular wall andfacilitates the perforation of both vascular walls concurrently, whileminimizing the quantity of tissue destruction that results. Carbondioxide is extremely soluble and therefore does not result in gasembolism. It has been previously shown (experimentally and clinically)that large volumes of compressed CO₂ gas can be introduced intravenouslyand intraarterially without incurring harmful effects in-vivo.

After the vascular wall perforation process has been satisfactorilycompleted and the AV fistula created at the chosen anatomic site, theradiofrequency current is disrupted; and the sliding electrode isdisengaged and withdrawn into the protective interior of the venouscatheter. The venous cutting tool is then withdrawn 2-5 mm proximallyrelative to the venous cylinder component while holding the arterialcatheter steady in its prior position within the artery. This act ofwithdrawing the venous cutting tool from the cylinder causes thetransvascular magnetic attraction to be broken while the arterialcatheter is maintained unchanged in its prior aligned position at theperforation site. Radiopaque contrast medium can then be injected intothe artery via the internal lumen of the arterial catheter; and the AVfistula assessed fluoroscopically. Evidence of extravasation at thefistula site can therefore be ruled out as well.

The result of this methodology and procedure is the generation of an AVfistula on-demand between closely associated arteries and veins at acarefully chosen and verified vascular anatomical site in-vivo. Theradiologist can halt the sequence of steps at any time prior toactivating the vascular wall perforation means (the radiofrequencyelectrode circuitry in this preferred embodiment) without risk or hazardto the patient or the peripheral blood circulation in any substantialmanner. Moreover, the methodology allows the radiologist to repeatedlyassess, verify, and confirm his choices of anatomical site location;note the alignment and positioning of the arterial catheter as well asthe alignment orientation and positioning of the venous catheter; andachieve the proper result and consequence of transvascular magneticattraction which results in changes in position for one or both of thecatheters in-vivo--all which occur prior to engaging the means forphysically perforating the vascular walls and generating an aperturebetween the artery and the adjacently positioned vein.

VI. Illustrative Applications and Usages

A number of intended applications and exemplary usages are brieflydescribed below. Each of these is merely one representative instance ofuse for the present invention; and many other applications existpresently where the catheter apparatus can be advantageously employedfor the benefit of the patient.

A. Hemodialysis Access

A major advantage of the PAVFC technique is the avoidance of a surgicalprocedure. As stated earlier, renal failure patients have impaired wouldhealing, and an increased incidence of wound infections. In addition,renal failure is associated with modest degrees of immunosuppression. Assuch, wound infections can lead readily to sepsis and potentially fatalcomplications. A technique that permits creation of hemodialysis accesswithout necessitating an incision is very attractive. In addition, theprocedure would not require an anesthetic and anesthesiologist, oroperating room time and personnel, and could therefore be performed atlower cost.

For reasons discussed earlier, a fistula is preferred over a prostheticarteriovenous shunt. Unfortunately, however, surgical access is oftenlimited to the distal radial artery; and often, there is not a vein ofsufficient size in this area. The PAVFC technique allows fistulaformation in areas where surgical exposure would be problematic. Assuch, there are more potential sites available. This allows a more idealfistula to be created, without the risk of venous kinking.

The PAVFC technique allows evaluation of the juxta arterial venoussystem of the entire extremity by intravascular ultrasound to identifythe most favorable anatomic site and provides accurate assessment ofvenous diameter. Veins on which surgical anastomosis would be difficultdue to small size or thin walls are easily addressed and utilized by thePAVFC. More importantly, the vessels are not dissected out ormanipulated, preserving the tenuous vaso vasorum, which will improvepatency.

Potential problems with this technique are few, and relate primarily tothe risk of hemorrhage. If an anatomically favorable site is selected,this risk will be quite small. In the event of hemorrhage, an expandinghematoma in the arm is clinically obvious, and is readily controlledwith the direct pressure using a blood pressure cuff or manualcompression. It may prove necessary to surgically explore patients inwhom compression proves inadequate. The risk of using intravenouscontrast to facilitate fluoroscopic visualization of arm venous anatomyis small, as is the risk of intraarterial contrasts to assist adequacyof the AV fistula post-procedure.

B. Portal Venous Hypertension And Veno-Venous Fistulae

Portal venous hypertension develops as a complication of end stagecirrhosis, and other forms of liver disease. The portal veins drain fromthe intestine to the liver. The blood is filtered through the liverbefore entering the systemic venous system, and returning to the heart.When the liver becomes badly diseased, resistance to portal venous flowincreases. The filter mechanism becomes "clogged". As a result, thepressure in the portal venous systemic increases, which results inmassive dilation of the naturally occurring portal-systemic venousconnections.

One such area of portal-systemic venous connection is at thegastroesophageal junction (near the top of the stomach). These thinwalled, massively dilated veins often rupture spontaneously, resultingin exsanguinating upper gastrointestinal hemorrhage, which is frequentlylethal. Surgical therapy is directed at lowering the portal venouspressure by creating a shunt between the portal vein or it's majorbranches, and the i systemic venous system, usually the inferior venacava. The operation is effective in lowering portal venous pressure inmost patients, and usually prevents additional bleeding episodes. Theprocedure is, however, quite risky. Patients with advanced liver diseasetolerate surgery poorly, with reported operative mortality of 10%, 50%,and 80% for portalcaval bypass in patients with early, intermediate, andlate stage liver failure, respectively.

Percutaneous creation of portal-systemic connection has been performedat many institutions with some success. The current technique, however,does not permit identification of closely adjacent portal and systemicveins, does not utilize magnetic attraction to bring the adjacent veinsinto close proximity, and does not utilize radiofrequency current, laserenergy, or static discharge to create the connection. Each of thesemodification of the current percutaneous technique represents a majortechnical advance, and will result in a larger portosystemic connection,and better portal venous decompression. As such, the PAVFC catheter andtechnique is extremely useful in this field. One catheter is introducedvia the femoral or jugular vein and is advanced into the inferior venacava to the level of the portal vein. The second catheter is introducedinto the portal venous system by way of percutaneous transhepaticpuncture or by transjugular-hepatic approach. Proximity of the twocatheters is achieved with intravascular ultrasound and fluoroscopy, asdescribed for dialysis access. A variety of veno-venous fistulae can begenerated in this manner.

C. Creation of Graft Material

The PAVFC catheters and technique are useful in the creation of suitableconduit, or graft material, in anticipation of subsequent MinimallyInvasive Coronary Artery Bypass Grafting (MICABG). MICABG is a rapidlyevolving technique that allows blocked coronary arteries to be bypassedwithout necessitating cardiopulmonary bypass or cardiac arrest.

Traditionally, when a patient develops critical narrowing of thecoronary arteries not amenable to medical management or angioplasty, aconventional coronary artery bypass is performed. The patient's chest isopened, and the heart attached to the heart lung machine by way of largecannula inserted in the aorta and right atrium. The heart lung machinepumps and oxygenates the blood, enabling the surgeon to temporarilyarrest the heart by mechanical and pharmacological means, withoutinterrupting blood flow to the brain, kidneys, and other vital organs. Aclamp is placed on the ascending aorta, which deprives the heart ofblood and results in cessation of cardiac activity. The clamp alsoallows the proximal ends of segments of saphenous vein, harvested fromthe patient's leg, to be attached to the aorta in a blood freeenvironment. The distal ends of the vein grafts are attached to thecoronary arteries beyond the areas of critical narrowing. Some coronaryarteries are bypassed with the left or right internal mammary arteries.Long term patency of mammary grafts is much better than that seen withvein grafts. In addition, no proximal anastomosis is necessary as themammary arteries are already branches of the arterial tree, andtherefore carry arterial flow despite leaving the proximal artery insitu. The crossclamp is then removed, and blood flow restored to theheart.

MICABG is a new method of surgical revascularization that has thepotential of being less risky than conventional bypass. Most, if notall, of the morbidity associated with conventional coronary arterybypass is related to cardiopulmonary bypass and temporary cardiacarrest. The MICABG technique allows the surgeon to graft the coronaryarteries without necessitating these maneuvers. MICABG is not withoutlimitations, however. With this technique, the heart continues to beat,and eject blood at high pressure and flow through the ascending aorta.As such, it is not currently possible to attach vein grafts to theaorta. All grafting must therefore be performed with arteries as they donot require proximal anastomosis. Thoracic arteries suitable for use asgrafts are, unfortunately, in short supply. Only the left and rightinternal mammaries are of adequate diameter and length to be of use. Thegastroepiploic artery can be used for grafting, but requires alaparotomy for harvest, and is technically more demanding.

The PAVFC catheters and technique are of use in patients undergoingMICABG. Each of the 12 paired ribs has closely associated with it aneurovascular bundle. This bundle contains a sensory nerve, an artery,and a closely associated vein. The artery measures only 1 to 1.5 mm indiameter, and as such, is of inadequate diameter to be used as a graft.If, however, a fistula is created between the distal intercostal arteryand vein, both thin walled vessels will dilate with time. This dilationof intercostal arteries from increased flow is observed clinically inpatients with coarctation of the aorta. Patients electively scheduled toundergo MICABG could have distal intercostal fistulas created in one ormore of the larger intercostal arteries with the PAVFC technique,approximately, 6 weeks prior to anticipated heart surgery.

What we claim is:
 1. An intervascular fistula generating catheterapparatus for percutaneous introduction through a perforation in a bloodvessel wall, extension within a blood vessel in-vivo, and generation ofa fistula on-demand between closely associated blood vessels at a chosenanatomic site in-vivo, said intervascular fistula generating catheterapparatus comprising:a hollow sheath for percutaneous introductionthrough a perforation surgically created in a wall of a blood vesselin-vivo; and a fistula generating vascular catheter suitable forpercutaneous introduction through a perforation in a wall of a bloodvessel via said hollow sheath and subsequent extension within a bloodvessel in-vivo to a chosen anatomic site, said fistula generatingvascular catheter being comprised of (a) a vascular catheter tubesuitable for entry through a vascular wall perforation and subsequentextension within a blood vessel in-vivo, said tube having a fixed axiallength, a discrete proximal end, a discrete distal end, and at least oneinternal lumen of predetermined volume, (b) a distal end tube tipadapted for entry through a perforation in a vascular wall andintravascular guidance of said vascular catheter tube within a bloodvessel in-vivo to a chose anatomic site, (c) discrete magnet meanspositioned within said internal lumen of said vascular catheter tube atsaid distal end and set in axial alignment with said distal end tubetip, said discrete magnet means having sufficient magnetic force tocause an adjustment in intravascular position for said vascular cathetertube when in proximity with a source of magnetic attraction thendisposed within a closely associated blood vessel, (d) vascular wallperforation means positioned within said internal lumen of said vascularcatheter tube at said distal tube end adjacent to but separate from saidmagnet means and set in axial alignment with said distal end tube tip,said vascular wall perforation means becoming adjusted in positionwithin the blood vessel via the magnetic force of said magnet means whenin magnetic proximity with a source of magnetic attraction then disposedwithin a closely associated blood vessel in-vivo, and (e) remoteactivation means for activating said vascular wall perforation means ofsaid vascular catheter tube on-demand wherein said vascular wallperformation means perforates the vascular walls of the closelyassociated blood vessels at the chosen anatomic site to generate afistula in-vivo between the closely associated blood vessels.
 2. Anintervascular fistula generating catheter apparatus for percutaneousintroduction through a perforation in a blood vessel wall, extensionwithin a blood vessel in-vivo, and generation of a fistula on-demandbetween closely associated blood vessels at a chosen anatomic sitein-vivo, said intervascular fistula generating catheter apparatuscomprising:a pair of hollow sheaths for individual percutaneousintroduction through a performation surgically created in the walls oftwo different blood vessels in-vivo; a pair of fistula generatingvascular catheters suitable for individual percutaneous introductionthrough a perforation in a wall of a blood vessel via said hollowsheaths and subsequent extension individually within different bloodvessels wherein at least one of said vascular catheters is comprised of(a) a vascular catheter tube suitable for entry through a vascular wallperforation and subsequent extension within a blood vessel in-vivo, saidtube having a fixed axial length, a discrete proximal end, a discretedistal end, and at least one internal lumen of predetermined volume, (b)a distal end tube tip adapted for entry through a perforation in avascular wall and intravascular guidance of said vascular catheter tubewithin a blood vessel in-vivo to a chosen anatomic site, (c) discretemagnet means positioned within said internal lumen of said vascularcatheter tube at said distal end and set in axial alignment with saiddistal end tube tip, said discrete magnet means having sufficientmagnetic force to cause an adjustment in intravascular position for saidvascular catheter tube when in proximity with a source of magneticattraction then disposed within a closely associated blood vessel, (d)vascular wall perforation means positioned within said internal lumen ofsaid vascular catheter tube at said distal tube end adjacent to butseparate from said magnet means and set in axial alignment with saiddistal end tube tip, said vascular wall perforation means becomingadjusted in position within the blood vessel via the magnetic force ofsaid magnetic means when in proximity with a source of magneticattraction then disposed within a closely associated blood vesselin-vivo, and (e) remote activation means for activating said vascularwall perforation means of said vascular catheter tube on-demand whereinsaid vascular wall perforation means perforates the vascular walls ofthe closely associated blood vessels at the chosen anatomic site togenerate a fistula in-vivo between the closely associated blood vessels;and wherein the other of said fistula generating vascular catheter pairis comprised of (a) a vascular catheter tube suitable for entry througha vascular wall perforation and subsequent extension within a bloodvessel, said tube having a fixed axial length, a discrete proximal end,discrete distal end, and at least one internal lumen of predeterminedvolume, and (b) a source of magnetic attraction positioned within saidinternal lumen of said vascular catheter tube.
 3. An intervascularfistula generating catheter apparatus for percutaneous introductionthrough a perforation in a blood vessel, extension within a blood vesselin-vivo, and generation of a fistula on-demand between closelyassociated blood vessels at a chosen anatomic site in-vivo, saidintervascular fistula generating catheter apparatus comprising:a pair ofhollow sheaths for individual percutaneous introduction through aperforation surgically created in the walls of two different bloodvessels in-vivo; a pair of fistula generating vascular catheterssuitable for individual percutaneous introduction through a perforationin a wall of a blood vessel via said hollow sheaths and subsequentextension individually within different blood vessels comprising a firstvascular catheter comprised of (a) a first vascular catheter tubesuitable for entry through a vascular wall perforation and subsequentextension within a blood vessel in-vivo, said first tube having a fixedaxial length, a discrete proximal end, a discrete distal end, and atleast one internal lumen of predetermined volume, (b) a first distal endtube tip adapted for entry through a perforation in a vascular wall andintravascular guidance of said first vascular catheter tube within ablood vessel in-vivo to a chosen anatomic site, (c) first discretemagnet means positioned within said internal lumen of said firstvascular catheter tube at said distal end and set in axial alignmentwith said first distal end tube tip, said first discrete magnet meanshaving sufficient magnetic force to cause an adjustment in intravascularposition for said first vascular catheter tube when in magneticproximity with a source of magnetic attraction then disposed within aclosely associated blood vessel in-vivo, (d) a first component ofvascular wall perforation means positioned within said internal lumen ofsaid first vascular catheter tube at said first distal tube end adjacentto but separate from said first magnet means and set in axial alignmentwith said first distal end tube tip, said first component of vascularwall perforation means and said first vascular catheter tube becomingadjusted in position within the blood vessel via the magnetic force ofsaid magnetic means when in proximity with a source of magneticattraction then disposed within a closely associated blood vesselin-vivo, and (e) remote activation means for activating said firstcomponent of vascular wall perforation means of said first vascularcatheter tube on-demand in-vivo such that a fistula is generated betweenclosely associated blood vessels at the chosen anatomic site; and asecond vascular catheter comprised of (a) a second vascular cathetertube suitable for entry through a vascular wall perforation andsubsequent extension within a blood vessel in-vivo, said second tubehaving a fixed axial length, a discrete proximal end, a discrete distalend, and at least one internal lumen of predetermined volume, (b) asecond distal end tube tip adapted for entry through a perforation in avascular wall and intravascular guidance of said second vascularcatheter tube within a blood vessel in-vivo to a chosen anatomic site,(c) second discrete magnet means positioned within said internal lumenof said second vascular catheter tube at said second distal end and setin axial alignment with said second distal end tube tip, said seconddiscrete magnet means being a source of sufficient magnetic force tocause an adjustment in intravascular position for said second vascularcatheter tube when in magnetic proximity to said first discrete magneticmeans of said first vascular catheter in-vivo, and (d) a secondcomponent of vascular wall perforation means positioned within saidsecond vascular catheter tube at said second distal tube end adjacent tobut separate from said second discrete magnet means and set in axialalignment with said second distal end tube tip, said second component ofvascular wall perforation means becoming adjusted in position within theblood vessel via the magnetic force of said second magnetic means ofsaid second vascular catheter tube and acting in concert with said firstcomponent of vascular wall perforation means to generate a fistulaon-demand between closely associated blood vessels in-vivo at the chosenanatomic site.
 4. The intervascular fistula generating catheterapparatus as recited in claim 1, 2, or 3 wherein said magnet meanscomprises at least one rare earth magnet.
 5. The intervascular fistulagenerating catheter apparatus as recited in claim 1, 2, or 3 whereinsaid magnet means comprises at least one electromagnet.
 6. Theintervascular fistula generating catheter apparatus as recited in claim1, 2, or 3 wherein said vascular well perforation means is selected fromthe group consisting of radiofrequency electric circuitry means, staticelectricity discharge means, mechanical cutting means, and laser lightenergy carrying means.